Nessler's reagent
Encyclopedia
Potassium tetraiodomercurate(II) is an inorganic compound containing potassium cations and the tetraiodomercurate(II) complex anion. It is mainly used as Neßler's reagent, a 0.09 mol/L solution of potassium tetraiodomercurate(II) (K2[HgI4]) in 2.5 mol/L potassium hydroxide, used to detect ammonia
.
, when this solution gives a yellow coloration, it indicates the presence of ammonia: at higher concentrations, a brown precipitate may form. The sensitivity as a spot test is about 0.3 μg NH3 in 2 μL.
Nessler's reagent is generally prepared from potassium iodide
and mercury(II) chloride
. A hot concentrated solution of mercury(II) chloride
is added to concentrated solution of potassium iodide, until the precipitate of mercury(II) iodide stops dissolving. The liquid is filtered, and potassium hydroxide
and a further bit of mercury(II) chloride solution are added. The resulting solution is then cooled and diluted to required concentration. Nessler's reagent may be used with Nessler tubes.
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
.
Nessler's reagent
Named after Julius NeßlerJulius Neßler
Julius Neßler was a German chemist.He discovered the Nessler's reagent.- Biography :Neßler studied at the University of Freiburg from 1853 to 1856, when he attained his PhD. After his Ph.D...
, when this solution gives a yellow coloration, it indicates the presence of ammonia: at higher concentrations, a brown precipitate may form. The sensitivity as a spot test is about 0.3 μg NH3 in 2 μL.
- NH4+ + 2[HgI4]2− + 4OH− → HgO·Hg(NH2)I + 7I− + 3H2O
Nessler's reagent is generally prepared from potassium iodide
Potassium iodide
Potassium iodide is an inorganic compound with the chemical formula KI. This white salt is the most commercially significant iodide compound, with approximately 37,000 tons produced in 1985. It is less hygroscopic than sodium iodide, making it easier to work with...
and mercury(II) chloride
Mercury(II) chloride
Mercury chloride or mercuric chloride , is the chemical compound with the formula HgCl2. This white crystalline solid is a laboratory reagent and a molecular compound. It is no longer used for medicinal purposes Mercury(II) chloride or mercuric chloride (formerly corrosive sublimate), is the...
. A hot concentrated solution of mercury(II) chloride
Mercury(II) chloride
Mercury chloride or mercuric chloride , is the chemical compound with the formula HgCl2. This white crystalline solid is a laboratory reagent and a molecular compound. It is no longer used for medicinal purposes Mercury(II) chloride or mercuric chloride (formerly corrosive sublimate), is the...
is added to concentrated solution of potassium iodide, until the precipitate of mercury(II) iodide stops dissolving. The liquid is filtered, and potassium hydroxide
Potassium hydroxide
Potassium hydroxide is an inorganic compound with the formula KOH, commonly called caustic potash.Along with sodium hydroxide , this colorless solid is a prototypical strong base. It has many industrial and niche applications. Most applications exploit its reactivity toward acids and its corrosive...
and a further bit of mercury(II) chloride solution are added. The resulting solution is then cooled and diluted to required concentration. Nessler's reagent may be used with Nessler tubes.